The public broadband switching network VBN of the German Bundespost permits transmission of image and audio in television quality, at a bit rate of 140 mbit/s. The VBN represents a direct dial broadband network for a large number of subscribers with broadband terminals, such as video telephones and video conferencing equipment. Each subscriber is coupled to the VBN via a subscriber line unit TAE which converts the 140 mbit/s signals into video, audio, and data signals. A broadband private automatic branch exchange may also be connected to the VBN via such a subscriber line unit. This prior art broadband private automatic branch exchange consists of a video switching array, an audio switching array, and a central controller. Up to 15 user stations may access video communication on the VBN via this exchange. For this, each broadband terminal includes its own video telephone controller and a separate operator position for controlling call setup and for signaling in the VBN (P. Pernsteiner, F. Brendel, NTZ, Vol. 42 (1989), No. 8, pp. 486-493).
Through the separate operator position associated with each broadband terminal, one subscriber line unit TAE is available for use by 15 user stations; however, functions characteristic of a private automatic branch exchange, i.e., arbitrary internal and external calls, are not possible for any of them.